This invention relates to the electrical resistance welding of lead-acid storage battery intercell connectors by the Extrusion-Fusion process described in United States Patent application Ser. No. 134,442 entitled "Through the Partition Connection Formed by an Extrusion-Fusion Technique" filed Apr. 15, 1971, in the names of Robert C. Matter and Donald K. Aldred, and assigned to the assignee of the present invention. More specifically, this invention improves that process by the use of particular welding conditions and lead alloys which combine to provide a reliable readily controllable manufacturing-scale process, and strong, substantially void-free intercell connectors. Moreover, this invention provides apparatus for carrying out the improved process.
Basically the Extrusion-Fusion process (Ser. No. 134,442) makes liquid-tight, low resistance, electrical connections between adjacent cells of a multi-cell lead-acid storage battery by: clamping two thick plate strap lugs tightly against an intercell partition having an aperture in it; squeezing two welding electrodes together through holes in the clamp to extrude lug metal out of the thick lugs into the aperture until contact is made therein; and passing welding current through the extruded metal to melt it and, under the continuing force of the electrodes, cause it to flow into any voids in the aperture while, at the same time, extruding more metal out of the lugs into the aperture until the aperture is packed full of lug metal. With the clamping and electrode forces still applied, the weld nugget is allowed to cool and solidify.
Among the problems with production-scale implementations of the Extrusion-Fusion process is assuring consistency from one weld to the next over an extended production run and to provide simple quality control techniques for monitoring the welding conditions and the product produced. Conventional non-destructive tests (e.g., air leak and IR drop) have not demonstrated sufficient sensitivity to detect poor quality welds and alter the operator that welding conditions should be corrected. The expression "welding conditions" is intended to include principally clamping force, electrode force and response (i.e., follow-through), welding current and welding time. One aspect of this invention relates to a reliable quality control tool for monitoring the welding conditions.
Another problem with production-scale implementations of the process is minimizing the variable affecting the process and insuring that the remaining variables (i.e., the welding conditions) are controllable and have sufficiently broad operating ranges that the process may be operated continuously for extended periods of time without requiring frequent corrections and adjustments. Another aspect of this invention solves this problem while at the same time it substantially eliminates the formation of voids in the weld and produces welds having exceptionally high torque test values.
An object of this invention is to provide a manufacturing-scale version of the Extrusion-Fusion process and apparatus for reliably carrying it out which: consistently produces strong, splatter-free, substantially void-free intercell connections over a sufficiently broad range of welding conditions to permit continuous operation with only occassional process monitoring by sample destruction; and produces a reliable, readily-observable indicator of the welding history of the connection and hence a manifestation as to whether welding condition adjustments are needed.